Flexible grinder



April 18, 1939. L. CHURGIN FLEXIBLE GRINDER Filed NOV. 17, 1937 IN OR.

ATTORNEY Patented Apr. 18, 1939 UNITED STTES --AT E OF F 1 CE 3 Claims.

My present invention is shown as embodied in a simple device which relates more particularly to grinders adapted for use in the mechanical dental industry. While particularly adapted for 5" use in the mechanical dental industry, it is useful and adaptable to numerous other industries such as jewelry, pattern, tool, cabinet and furniture manufacture; for sanding, polishing of objects of art, buttons, combs, pocketbook frames, ornaments made of wood, metals and plastics such as celluloid, casein and phenolic condensation products, plaster of Paris, ceramics, soapstone, semiprecious gems and other novelties commercially r produced where it is desirable to change the contour, remove portions of the outer surface,

smoothen or polish, particularly other than surfaces in a true plane.

The object is to provide an abrasive surface that will conform to certain irregularities of shape of the object to be ground within the limitations of the grinding or abrasive material; and to provide easy and rapid means of replacement and substitution of the grinding surface. To this end, my invention comprises one or two thin discs of paper or cloth coated with abrasive material, backed by a disc of fiemble rubber and means for rotating the rubber and abrasive in an assembled manner, so that when objects are pressed against the abrasive material, a grind-' mg operation is performed.

In a preferred form, the invention is embodied in a structure including a flexible disc flanked by two sheets of grinding material attached to one end of a collet or chuck and held in place by means of a screw, the other end of the collet being provided with a bayonet slot attachable to a rotating spindle of a lathe. It will be evident that the use of the flexible disc to back an abrasive sheet permits those versed in the art and technique to grind, sand or polish with greater nicety and smoothness of contour due to the natural conformity to various shapes.

Other features and advantages will appear upon consideration of the following description and of the drawing, in which:

Fig. 1 is a longitudinal view partly in section, in the plane of the axis of rotation of the grinder, showing the constituent parts as used and assembled.

Figure 2 is a longitudinal sectional view of another adaptor.

Fig. 3 is a longitudinal view of a simpler form of the grinder to be used in an ordinary drill chuck.

In this drawing I is a flexible disc preferably of rubber, 2 and 2 are preferably discs of emery paper with the abrasive surfaces facing away fromthe flexible disc. The abrasive surfaced discs with the flexible rubber disc between them, are clamped through their center to an arbor or shaft extension so that upon the rotation of the shaft the discs will rotate at the same speed as the shaft.

In Fig. 1 the shaft extension takes the form of an interchangeable chuck comprised of An adaptor, 5, having on one end a thread, 8, that screws into the end of the motor or lathe shaft; adjoining the threaded end, a shoulder is provided for the purpose of tightening, the other end of which is a straight shank, 9, bored to hold a compression spring, I. On the straight shank a short distance from the shoulder, a pin, 5, is rigidly attached in a radial direction and protruding beyond the outer cylindrical surface of the shank, 9.

A sleeve or collet, 3, bored to a sliding fit over the shank, 9, and slotted in the manner shown, 10, to engage with pin, 6. On the other end of the collet, a tapping is provided for a cap screw, 4, for the purpose of clamping securely the two discs of emery paper with a flexible disc of rubber between them.

For the convenience of obtaining a better grip in securing, assembling and dismantling the various parts, I prefer to provide flat surfaces on the shoulder, 5, to fit a wrench, to knurl a portion of the exterior of the collet, 3, for better handling, and to either provide two holes for a spanner wrench or a slot for a screw driver in the head of the screw, 4.

In Fig. 2 is shown an adaptor, 5', provided with a tapping, 8', to screw onto an externally threaded lathe or motor shaft. The pin, 6, the diameter and length of the shank, 9, and the hole bored in the end of the shank to hold a compression spring, 1, are all standarized to fit interchangeable collets.

In both Figs. 1 and 2, the pin, 6, when engaging in slot, 10, by sliding collet, 3, over shank, 9, and compressing the spring, I, then turning slightly, locks the two units securely in what is referred to and known in the arts as a bayonet fastening. The direction of the portion of the slot at right angles to the axis is determined by the normal direction of rotation of the shaft, clockwise or counter-clockwise. When the shaft is rotating and the grinder is in use, the bayonet clutch will not open and permit the disengagement of the collet from the shank. The thread, 8, and the thread of the cap-screw, 4, are either in a right hand or left hand direction to likewise prevent loosening the respective units when in operation- The compression spring, 1, prevents the momentum of the discs, when rotating, from disconnecting the bayonet clutch when the motor is stopped.

A simpler modification suitable for use with a vertical spindle such as a drill press is shown in Fig. 3. Here the flexible disc, flanked by the sheets of abrasive discs, are attached to the threaded arbor, l5, by means of nuts, 16 and H. The arbor in turn is held in the drill chuck, l8.

It will be obvious that my invention essentially consists of a shaft extension, one or two discs of abrasive sheet material backed by a flexible disc, a means for holding the various parts in proper relation to each other so that when rotating in a predetermined direction, the entire assembly forms a safe and efiicient grinding device that in addition to ordinary grinding and polishing, will conform to certain contours of the object to be so treated. However, when it is so desired, upon the stopping of the rotation of the shaft, one may readily remove the abrasive disc assembly by separating the collet from the adaptor. By applying pressure along the axis of the spindle so as to slightly compress the spring in the end of the adaptor and by means of a slight twist in a direction opposite to the normal operating direction of rotation, the bayonet fastening is disengaged and the collet with the abrasive discs may be removed and may be substituted with similar collet having abrasives of different grits.

Where the flexible grinder is used in conjunction with a drill chuck as shown in Fig. 3, the chuck, I8, is readily opened by rotating the knurled collar and disengaging the arbor holding the abrasive discs. This permits the substitution of arbors with other discs, drills or any other tools intended to be used with the rotating spin- ,dle.

While the size of my device is not an essential feature and while relative sizes of parts may be varied within limits, it is an important feature that I have succeeded in embodying in a compact arrangement, elements useful forthe purpose of grinding, cutting, smoothening and polishing irregular surfaces.

While I prefer a flexible backing disc made of rubber, a disc of spring steel, brass or other material may be used. A soft, pliable disc may be used provided it has sufficient weight or is weighted at the periphery of the disc so that when rotated at a sufficient speed, it will tend to assume the characteristics of a flexible disc as a result of centrifugal force.

While I prefer carborundum-coated paper for an abrasive, aloxite, alundum, emergy, flint, garnet, sandpaper or cloth may be used; while for smoother surfacing and polishing, crocus, pumice, rouge, tripoli, etc. coated sheets may be used.

The rapid interchangeability of collets on the same adaptor, although not essential to the grinding operation, presents a decided manufacturing advantage in the use of the grinder, as it permits variations in the diameter of grinding discs, derees of roarseness or fineness of the abrasives, and rigidity or flexibility of the backing disc, without loss of time or use of many lathes or motor-driven spindles.

Other useful and valuable parts of my invention are the easy replaceability of worn off or undesirable abrasive sheets with other abrasive discs by a simple means such as a single screw, the fact that only the portion of the abrasive disc clamped between the head of the screw and the collet are secured to the flexible disc, and that the independent flexibility of the abrasive disc is not impaired by being cemented to the flexible backing disc.

Variations in the structural details described in my specification may be made without deviating from the true scope and spirit of the invention.

I claim:

1. A grinder including a grinder assembly comprising an elastic flexible disc backing a layer of abrasive material, an arbor centrally engaging said disc, and means for rigidly holding together said disc and arbor with the axis of the arbor substantially perpendicular to the plane of the disc; in combination with a shaft extension and adapter detachably connected to said grinder assembly by pin and bayonet slot and said adapter being hollow and provided with a compression spring applying endwise thrust upon the pin member and the slot member to prevent uncoupling of the bayonet joint when subjected to endwise pressure during grinding.

2. A grinder including an elastic flexible backing disc and one or more flexible discs coated with abrasive material, an arbor and means for clamping the central portions of the elastic backing disc and the flexible abrasive disc upon said arbor, and means for detachably securing said arbor to a driving shaft, including a tubular adapter on.

one of said members, having a bayonet slot formed in the end thereof, and a cooperating tubular member having a bayonet pin adapted for engagement with said slot, together with a spiral spring within said tubular members adapted to be axially compressed when said bayonet slot engages said pin.

3. A grinder including a flexible grinding disc, an arbor to which the central portion of said disc is secured, and detachable coupling members for attaching the arbor to a drive shaft, said detachable members being provided one with aradially set pin, and the other with a hook shaped bayonet slot, and a compression spring arranged to exert endwise pressure, in opposite directions onsaid members so as to hold them in locked position when rotating and subjected to endwise pressure during grinding operations.

LEOPOLD CHURGIN. 

